function createButton(func) {
    var wrapper = document.getElementsByClassName('mt-5')[0];
    var context = wrapper.getElementsByClassName('col-4')[1];
    var button = document.createElement("input");
    button.type = "button";
    button.value = "open";
    button.onclick = func;
    wrapper.appendChild(button);
}

window.onload = function() {
    createButton(function() {
        var url = document.getElementsByName('start-url')[0].value;
        window.open(url)
    });
};